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WORLD INTELLECTUAL PROPERTY ORGANIZATION

International Bureau

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(51) International Patent Classification 5 :

A61F 5/01, B25J 13/08
G05B 13/00

(11) International Publication Number: WO 92/13504

(43) International Publication Date: 20 August 1992 (20.08.92)

(21) International Application Number:

PCT/US92/00369

(22) International Filing Date :

16 January 1992(16.01.92)

(30) Priority data:

648,733

31 January 1991(31.01.91) US

(71) Applicant: MASSACHUSETTS INSTITUTE OF TECH-

NOLOGY [US/US]; 77 Massachussetts Avenue, Cam-
bridge, MA 02139 (US).

(72) Inventor: MAXWELL, Scott, M. ; 250 Mercer Street,

#C317, New York, NY 10012 (US).

(74) Agents: REYNOLDS, Leo, R. et al.; Hamilton, Brook,
Smith & Reynolds, Two Militia Drive, Lexington, MA
02173 (US).

(81) Designated States: AT (European patent), BE (European
patent), CA, CH (European patent), DE (European pa-
tent), DK (European patent), ES (European patent), FR
(European patent), GB (European patent), GR (Euro-
pean patent), IT (European patent), JP, LU (European
patent), MC (European patent), NL (European patent),
SE (European patent). _

Published

With international search report.

Before the expiration of the time limit for amending the
claims and to be republished in the event of the receipt of
amendments.

(54) Title: A SYSTEM FOR RESISTING LIMB MOVEMENT

ARM

102a

iOO

206

I LIMB COUPLER
j CUFF

212

POSITIONAL
VELOCITY
SENSORS

2.00

204

FORCE

TORQUE

SENSOR

LINKAGE

REDUCERS — .

j BRAKES

210

202

208

COUNTERBALANCES

PROCESSOR

106

(57) Abstract

A six degree of freedom limb movement resistance system is described in which a linkage system (200) of links (338-366)
and joints (300-334) couples a fixed point in space to a movable endpoint (E) of the linkage (200). A limb coupling cuff (212, 376)
is attached to the end point (E). Variable resistance force can be applied to the linkage (200) via computer controls (104, 106)
through a feedback path from position and velocity sensors (206). The linkage endpoint force acting to resist limb motion is in a
direction opposite to the endpoint velocity vector.

/•O/e 7H£ PURPOSES OF INFORMATION ONLY

Codes used lo identify Slates

party

to the PCI on the fiont pages of pamphlets publishing international

applications under the PCI*.

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NI-

Netherlands

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HIJ

Hungary

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of Korea

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t ice lite ostein

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Spain

Madagascar

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A SYSTEM FOR RESISTING LIMB MOVEMENT

Background Art

Orthoses, or limb assistive devices, have been
developed to assist disabled persons in performing

5 daily functions. One application for such devices
is in stabilizing limb motion in tremor patents.

The presence of random involuntary limb
movement superimposed on purposeful limb movement is
an abnormal condition that afflicts hundreds of

10 thousands of patients suffering from a variety of
diseases. Many tremor patients are disabled by
these involuntary movements due to the fact that the
amplitude of these movements is large enough to
degrade or obscure voluntary movement attempted by

15 the patient. Cerebral palsy patients suffering from
athetosis may also be disabled by their involuntary
limb movement. Chorea is another such condition.

In each of these cases, patients typically try
to overcome the disability imposed by the

20 involuntary movements of a particular limb, either
by steadying the motion using an unafflicted limb,
by jamming the afflicted limb against the body so as
to restrict its vibration, or even by having another
person grasp the limb to steady its motion. Drug

25 therapies and surgery have been attempted with

limited effectiveness and considerable risk for the
patient.

However, in the past ten years or so, a number
of orthoses have been developed for selectively

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suppressing random involuntary movements. These
devices are based on the observation that
significant reduction of the involuntary movements
can be achieved by the application of viscous

5 damping to the afflicted limb or body segment.

One such device is a one degree-of-f reedom
(DOF) orthosis with an electronically-controlled
magnetic particle brake used to retard limb motion
(See Dunfee, D.E., "Suppression of Intention Tremor

10 by Mechanical Loading", M.S. Thesis, M.I.T.
Department of Mechanical Engineering, February
1979) . This device, meant primarily for conducting
experiments on the wrist, prevents the patient from
performing whole-arm functional activities, since

15 limb motion is rigidly constrained in the remaining
DOF's.

Another prior art device is a 2 degree-of-
f reedom joystick used as a control interface to
electrical devices (such as powered wheelchairs)
20 while applying a resistive load to the limb. This
system also cannot be used for whole-arm movements
and is not meant as a general purpose functional
orthosis .

Despite such work, a need exists for an
25 orthosis which will enable full-arm movement, which
requires six degrees of freedom in a safe and
reliable manner. Such a device would be useful not
only for tremor suppression, but would also find
application in physical therapy and exercise
30 machines, especially if the device were capable of

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achieving force-velocity colinearity.
Force-velocity colinearity occurs when a force is
applied to a device endpoint and the device moves in
the direction of the force; resulting in a natural
cause and effect result.

Summary of the Invention

The invention consists of a system for
resisting the motion of a subject's limb about six
DOF's, and comprises a passive manipulator that can
be used in conjunction with a microcomputer, a
display monitor and electronic circuitry to process
manipulator outputs for use by the microcomputer.
The manipulator comprises a plurality of links,
joined together by revolute joints to form a linkage
system between a fixed point in space and a movable
endpoint of the linkage. As the endpoint of the
linkage is moved by the subject's limb, the joints
of the linkage — and hence, the links themselves —
rotate .

The rotation of certain joints in the linkage
are resisted by a plurality of brakes (such as
particle brakes) . These joints allow translational
motion of the endpoint in three DOF's and rotational
motion of the endpoint about each of three mutually
orthogonal axes. The limb (an arm) is coupled to
the manipulator endpoint by a limb coupling cuff,
the motion of the limb is resisted in six DOF's
(three translational, three rotational) .

The manipulator endpoint force acting to resist
the arm motion is in a direction opposite the

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endpoint velocity vector , resulting in substantial
force-velocity colinearity (FVC) . FVC is attained
when the force the human arm imparts is in the same
direction as the desired movement.

5 Brief Description of the Drawings

Figure 1 is a block diagram of an example

therapeutic system in which the manipulator of the

invention may be used.

Figure 2 is a block diagram of the manipulator

10 of the invention.

Figure 3 depicts the links, joints,
force-torque sensor, limb coupling cuff and
counterbalance weights comprising the manipulator
linkage.

15 Figure 4 is a dynamic equivalent of the

manipulator linkage shown in Figure 3.

Figure 5 is a schematic of a magnetic particle

brake .

Figure 6 is a schematic of the transmission for
20 joint 300 of Figure 3 # depicting links, a particle
brake, a reducer and a potentiometer.

Figure 7 is a schematic of the transmission for
joints 308 and 314 of Figure 3, depicting links,
particle brakes, reducers and potentiometers.
25 Figure 8 is a schematic of the voltage divider

circuit equipped with a potentiometer to measure
position.

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Figure 9 illustrates the moving target and
Manipulator crosshair that appear on the display
monitor in the pursuit tracking task.

Figures 10a and 10b are the top view and cross-
sectional views, respectively, of the elastic
element and strain gauges of the force-torque
sensor.

Figures 11a and lib are the top and side views
of the strain gauges on a single spoke of the
elastic element.

Figures 12a and 12b are schematics of the
Wheatstone bridge circuits for the horizontal and
vertical components of the applied load.

Detailed Description of the Invention

A preferred embodiment of the invention will
now be described in connection with Figure 1. This
embodiment illustrates a six DOF device coupled to
an arm of a subject. However, it is to be
understood that the invention is not limited thereto
and may in fact have greater or fewer DOF's and may
be useful for coupling to other limbs. Also, it
should be noted that while the term "manipulator" is
used for convenience, the system is passive and the
subject does the "manipulating". The system only
restrains or resists forces exerted by the subject's
limb. The manipulator 100 of the invention is one
component in a physical therapeutic system comprised
of (1) the manipulator 100; (2) a human subject 102;

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(3) a microcomputer 104 primarily used to process
data and adjust resistive forces within the
manipulator; (4) electronics 106 to preprocess data
from the manipulator destined for the computer; and

(5) a computer monitor 108 to display a moving
ob j ect .

The manipulator 100 is shown in the block
diagram of Figure 2 wherein mechanical connections
are shown in dotted/ dashed lines and electronic
connections in solid. A linkage set 200, is
mechanically coupled to brakes 202 which restrain
the motion of certain joints in the linkage 200.
Reducers 204 amplify the torques produced by the
brakes 202. Position and velocity sensors 206
measure the angles about which certain joints have
been rotated and the angular velocities,
respectively. A force-torque sensor 208 yields
measurements of loads applied at the manipulator
endpoint. Counterbalances 210 compensate load
imbalances about certain joints and a limb coupling
cuff 212 couples the arm 102a to the manipulator
endpoint. Each of these components will now be
described in detail in the following sections:

I. Linkage

The manipulator linkage 200 of Figure 3
comprises a set of 15 aluminum tubes or 'links'
338-366 joined together by 18 revolute joints
300-334 that allow rotation of the links with

respect to one another. In the figure , the
butterfly-shapes ( t>o ) 300-306 represent one of four
joints having rotation axes lying in the plane of
the paper, while circles (O) 308-334 denote one of
fourteen joints having rotation axes normal to the
plane of the paper.

The composite linkage structure 200 permits
motion in six DOF's. The 6 DOF motion is more
clearly seen in the simplified dynamic equivalent of
Figure 3, shown in the manipulator linkage drawing
of Figure 4. In Figure 4, the rotation of joint 300
about its axis produces rotation in the ±<f>
directions of a standard spherical coordinate system
centered at joint 308. Joints 308 and 402 are
coupled by a trapezoidal linkage T (shown in Figure
3, but not in Figure 4). Rotation of the coupled
structure 308 , 402 , T about joint 308 causes
rotation of the manipulator linkage in the ±6
directions, and a combination of rotations of joints
308 and 402 causes translational movement in
approximately the ±r directions. Hence, joints 300,
308 and 402 are responsible for positioning the
manipulator endpoint in three dimensional space.
Note that the manipulator endpoint E, defined as
being the point at which the manipulator linkage 200
is coupled to the limb of the subject 102, roughly
corresponds to the distal end of link 408 of Figure
4.

Joints 404, 406 and 3 06 are used to change the
orientation of the manipulator endpoint E. Rotation
about the axis of the joints 404, 406, 306

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corresponds to rotation about each of three mutually
orthogonal axes of a coordinate system centered at *
joint 406. In other words, rotation of joint 404
produces roll motion at the endpoint, rotation of
5 joint 406 produces pitch motion at the endpoint, and
rotation of joint 306 produces yaw motion at the
endpoint.

The more complicated structure of Figure 3 is
the linkage structure that is preferred in the

10 present embodiment because of several practical
limitations that arise in the simpler six- joint
structure of Figure 4. For example, it is difficult
to obtain a rotationally-stif f system with the
simpler design. Size and weight limitations are

15 also present, and the system of Figure 4 would
suffer from backlash and chordal speed variation.

To overcome these limitations, a number of
auxiliary joints 302, 310, 312, 316-332 that are not
present in the Figure 3 structure are introduced in

20 the Figure 4 structure. While joints 300, 306 and
308 of Figure 4 correspond to single joints
designated by the same reference numbers as in
Figure 3, joints 402, 404 and 406 of Figure 4 are
implemented by sets of joints in Figure 3.

25 specifically, joint 402 corresponds to a coupling of
joints 308-314, joint 404 corresponds to the pair of
joints 302 and 304 and joint 406 corresponds to the
set of joints 316-334.

Referring back to Figure 3, link 336 is used to

30 couple the entire manipulator structure (and in

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particular, joint 300) to a fixed external surface,
such as a floor. Link 338 couples joints 300 and
308 together. Joint 308 is part of a trapezoidal
four-bar linkage T comprising the four links 342-348

5 with joints at the vertices (i.e., connecting pairs
of adjacent links in the trapezoid) . Namely, joints
308 and 314 connect link pairs 342, 344 and 344, 348
respectively, while joints 310 and 312 connect pairs
342, 346 and 346, 348 respectively. As the four

10 joints 308-314 rotate together appropriately, the
shape of the trapezoid is changed, thereby causing
the manipulator endpoint E to travel in
approximately the ±r direction of a spherical
coordinate system centered at joint 308 (i.e., along

15 the dotted line 368) . The current ±r direction is
determined by the values of the azimuth and
elevation angles <f> and 6 as determined by the
amounts that joints 300 and 308 have been rotated.
The remaining links and joints of the

20 manipulator of Figure 3 constitute a novel gimbal
link geometry referred to as the 'upper linkage, 7
which provides the three orientational DOF's
corresponding to joints 404, 406 and 306 of Figure
4. The upper linkage comprises three parallelograms

25 p , P 2 , P 3 of links and joints. In the central

parallelogram P 1# joints 302 and 304 are coupled to
either end of the trapezoidal linkage's link 348,
with both joints providing a roll motion for the
upper linkage. Attached to the other side of joint

30 302 is link 350, which joins with link 360 at joint

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322. Attached to the other side of joint 304 is
link 366, which meets link 354 at joint 326. JThe
fourth side of the central parallelogram consists
of link 352, which is attached to link 360 at joint

5 324 and to link 354 at joint 328.

The left parallelogram P 2 consists of links
350, 360, 362 and 364 and joints connecting adjacent
pairs of these links. Specifically, pairs of links
350 and 362, 362 and 364, 364 and 360, and 360 and

10 350 are joined by joints 320, 316, 318 and 322,
respectively. Note that links 350 and 360 of the
left parallelogram P 2 are merely extensions of the
same links of the central parallelogram P^
Finally, the upper right vertex of the left

15 parallelogram is coupled to the lower left vertex of
the central parallelogram P x at joint 322.

The right parallelogram P 3 has as its sides
links 352, 354, 356, and 358 and joints connecting
adjacent pairs of these links. Specifically, pairs

20 of links 352 and 354, 354 and 356, 356 and 358, and
358 and 352 are joined by joints 328, 330, 332 and
334, respectively. Note that links 352 and 354 of
the right parallelogram P 3 are merely extensions of
the same links of the central parallelogram P ± .

25 Finally, the lower left vertex of the right
parallelogram P. is coupled to the upper right
vertex of the central parallelogram P x at joint 328.

The upper linkage in Figure 3 simulates the
function of joint 406 in Figure 4 in that it

30 produces a pitch motion in which the effective

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rotation is about a rotation axis 370 located at the
intersection of links 366 and 372 if they were to be
extended, and normal to the plane of the paper. The
pitch motion is accomplished by deforming the
parallelograms P 2# P 3 from rectangles to
non-rectangles, with the deformation taking place as
the joints 316-334 rotate in unison.

Finally, link 358 extends past joint 334 and
couples with joint 306, which is responsible for
producing a yaw motion. The other side of joint 306
is connected to link 372, which consists of the
force-torque sensor 374 attached to the limb
coupling cuff 376 worn by the subject.

II. Controlled Brakes

Six joints of the manipulator are coupled to
controlled braking devices that resist manipulator
endpoint motions imparted by the user in each of the
six DOF's. The brakes for the DOF's corresponding
to joints 300, 308 and 306 are labelled Bl, B2 and
B3, respectively, of Figure 3 and are located near,
and coupled to, the joints of Figure 3 bearing the
same reference numerals, while the brakes B4, B5, B6
for the DOF's corresponding to joints 402, 404 and
406 of Figure 4 are located near joints 308, 302 and
316 of Figure 3, respectively. The last three
brakes are not near their respective joints but are
instead located at other joints primarily because
the alternate joint locations are better suited to
provide counterbalancing (see Section VII) .

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A variety of braking mechanisms may be used to
retard joint motion. These include electric motors,
hydraulic actuators, mylar brakes, and magnetic
particle brakes. In the present embodiment,
5 magnetic particle brakes are used. The choice was
motivated by the simplicity, reliability, low cost,
and ease of computer control associated with such
brakes .

A typical magnetic particle brake Bl is shown

10 in Figure 5, to consists of a disk 500 that is
attached to an output shaft 502. Note that in
joints lacking reducers, the axis A of the output
shaft 502 is the rotational axis of the joint (as
will be seen in Section III) . The disk 500 resides

15 in a cylindrical cavity 504 larger than the disk.
Powdered magnetic particles 506 are contained in the
gap surrounding the disk 500. A coil of wire 508 is
wound around the cylindrical cavity 504.

When an electrical current travels through the

20 coil 508, a magnetic field parallel to the

cylindrical axis of the disk 500 is produced in the
cavity 504. The magnetic particles 506 in the gap
align to form what resemble 'chains' in response to
the applied current, and these chains of particles

25 506 resist the motion of the disk 500 as it rotates
along with the output shaft 502 to which it is
attached, thereby retarding the rotation of the
output shaft 502 about the axis A and making the
joint stiffer. The particle brake has a resistive

30 torque approximately proportional to the current

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applied to coil 508, The braking strength may
therefore be controlled by varying the applied coil
current .

Placid Industries B115P magnetic particle brake
5 is a suitable brake for Bl, B2 and B3 , while model
B15P may be used for brakes B4, B5, and B6. Models
B115P and B15P have rated torques of 115 and 15
inch-lbs, respectively, at rated currents of 1/3 and
1/4 Amps, maximum speeds of 1800 and 2000 r.p.m. ,
10 and a de-energized drag of 25 and 5 ounce-inches,
respectively. The torque output of the first three
brakes may be amplified using reducers, as described
in the next section.

III. Reducers

15 Reducers 2 04 are used to amplify the torque

output of particle brakes Bl, B2, and B3 by
approximately four times using cable drive
transmissions. Figure 6 illustrates an exemplary
reducer transmission, i.e., the transmission for

20 joint 300. A capstan 600, made of aluminum and

having a diameter of about 8 inches, is attached to
link 338 (of Figure 3), and is coupled by a 1/8 inch
diameter nylon-covered aircraft cable 602 to a
smaller diameter capstan 604, which has a diameter

25 of 2 inches and is attached to the output shaft 606
of particle brake 1. The base 608 of particle brake
Bl is attached to link 336 (also see Figure 3) . The
rotation of link 338 occurs about a rotation axis
that coincides with the axis of symmetry of large

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capstan 600, and is retarded with a resistive torque
that is four times that produced by the particle
brake, per se. A position sensor, described in more
detail in Section IV, consisting of a potentiometer

5 614 with a rotatable tuning arm 610 is coupled by
pulley 612 to capstan 606. Rotation of the output
shaft 606 relative to the base 608 corresponds to a
rotation of link 338 relative to link 336. The
potentiometer tuning arm 610 of the position sensor

10 therefore indicates the amount that joint 300 (see
Figure 3 between links 338 and 336) has been
rotated .

Figure 7 illustrates the more complicated cable
drive transmissions that couple brakes B2 and B3 to
15 the linkage. As seen in Figure 7, joint 308 of
Figure 3 in fact consists of two joints,
corresponding to the intersection of links 338 and
342 and the intersection of links 342 and 344 of
Figure 3.

20 In joint a, link 338 is attached to an 8 inch

capstan 700, coupled by nylon-covered aircraft cable
702 to 2 inch capstan 704 which is attached to the
base 706 of a particle brake B2. The output shaft
708 of particle brake B2 is attached to a 2 inch

25 capstan 710, which is coupled by aircraft cable 712
to an 8 inch capstan 714 that is attached to link
342 of Figure 3 (not shown in Figure 7) . Hence
relative motion between the output shaft 708 and
base 706 of particle brake B2 corresponds to

30 relative motion between links 338 and 342 via the 2

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inch capstans 704, 710 and 8 inch capstans 700, 714,
with links 338 and 342 rotating about a rotation
axis labelled 716 in the figure. Conversely,
resistive torque produced by particle brake B2 is

5 amplified via capstan pairs 704, 700 and 710, 714 to
provide greater damping in the relative motion
between links 338 and 342, i.e., in joint a.

In joint 0, link 344 is attached to the base
718 of particle brake B3. The output shaft 708 of

10 particle brake B3, which coincides with the output
shaft of particle brake B2, is likewise attached to
2 inch capstan 710, which is in turn coupled via
aircraft cable 712 to the 8 inch capstan 714
attached to link 342 of Figure 3 (not shown in

15 Figure 7) . Consequently, relative motion between
the output shaft 708 and base 718 of particle brake
B3 corresponds to relative motion between links 342
and 344 via the 2 inch capstan 710 and 8 inch
capstan 714, with links 342 and 344 rotating about

20 rotation axis 716. Thus, resistive torque produced
by particle brake B3 is amplified via capstan pair
710, 714 to provide greater damping in the relative
motion between links 342 and 344, i.e., in joint 0.

IV. Posit ion/ Velocity Sensors
25 The six position/velocity sensors S1-S6,

located near and coupled to the manipulator linkage
joints 300, 308, 308, 304, 320 and 306 of Figure 3,
provide information as to the amounts that these
joints have been rotated (i.e., position

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information) and how fast they are rotating
(velocity information) . The position/velocity
sensors at the joints listed above correspond to the
DOF's associated with joints 300, 308, 402, 404, 406

5 and 306 of Figure 4, respectively, and are hereafter
referred to as position/velocity sensors S1-S6, for
convenience. Equivalently, position sensors S1-S6
indicate the angle between the following pairs of
links: 336 and 338, 338 and 342, 338 and 344, 348

10 and 366, 352 and 360, and 358 and 372. The velocity
sensors indicate the rate of change of these angles.

Referring back to Figure 6, a position sensor
consists of a 5K0 potentiometer 614 (such as the
Helipot model 6186-R5K L1.0 B604M potentiometer)

15 having a tuning arm 610 coupled to the output shaft
606 of the joint by means of a pulley, so that the
rotation of the output shaft 606 causes the tuning
arm 610 of the potentiometer to rotate. This
rotational action varies the resistance of the

20 potentiometer as measured across two of its leads
616. The value of the resistance Rp indicates the
amount that the joint has been rotated. The
resistance value is determined by connecting the
potentiometer leads 616 to a voltage divider circuit

25 comprising a voltage source E coupled in series with
a standard resistor R and the potentiometer value Rp
(as shown in Figure 8) and measuring the voltage e =

E R p / (R+R p ) •

A velocity measurement is obtained by

30 differentiating the measurement provided by the

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position sensor, using a well-known analog
differentiator circuit. Joints other than the six
joints mentioned, do not contribute to additional
DOF's, therefore, additional potentiometers at these
5 joints would provide no additional position and/or
velocity information.

v - Force-Torque Sensor

Referring back to Figure 3, the force-torque
sensor (FTS) 374 is located at the manipulator

10 endpoint E to measure the load applied by the limb
coupling cuff 376 on the manipulator endpoint in
each of the six DOF's. That is, three forces and
three torques are measured. As will be shown in
detail in connection with Figs. 10-12, this measure-

15 ment process consists of several distinct steps.
First, a sensing element senses the deformation of
an elastic element 1000 in response to an applied
load. An electrical circuit (Figure 12) converts
the output of the sensing element into an electrical

20 signal suitable for computer interfacing. Finally ,
a transformation is performed whereby the vector of
electrical measurements is mapped to a vector whose
elements are the applied forces and torques.

Shown in Figure 10 is the elastic element 1000

25 machined from 7075-T6 aluminum alloy. The elastic
element, has an overall diameter of 4 inches and an
overall thickness of 0.8 inches. The element
consists of four concentric annuli 1002-1008 having
different thicknesses, and four spokes 1010 each

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being spaced at 90 degree intervals radiating
outward from the center of the innermost annulus
1008. A number of holes 1012, 1014 are drilled into
the elastic element. Holes 1012 and holes 1014
5 accommodate screws securing a FTS cover plate and a
limb coupling cuff (not shown) , respectively to the
element 1000. Hole 1016 accommodates the output
shaft of particle brake B6 (i.e., the brake coupled
to joint 306) .

10 strain gauges 1018 attached to each of the

spokes of the elastic element sense deformations of
the element. Two groups (a vertical group and a
horizontal group) of four strain gauges are attached
to each spoke. In each group, each of the four

15 gauges is attached to a different edge of the spoke
(which has a square cross-section) .

In addition to sensing deformations, the strain
gauges also provide an electrical representation of
the deformation. Specifically, each strain gauge

20 has a nominal resistance of 120 0 which varies with
the sensed strain. Referring to Figure 11, four
strain gauges (a.k.a. variable resistors) 1100-1106,
two from each group on a particular spoke, are
electrically configured to form a Wheatstone bridge

25 circuit (see Figure 12). The voltage v 1 across the
bridge is measured. A nonzero value of v 1 indicates
unequal strain gauge resistance values. The
remaining four strain gauges on the spoke 1108-1114
(again, two from each group) also provide a voltage,

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v 2# in a similar manner. The two measured voltages
v 1 and v 2 provide information as to the horizontal
and vertical components of the applied force,
respectively. The strain gauges on the other three
5 spokes provide this voltage information in the same
way, therefore, a vector of voltages v = [v- v_ ...
v Q ] is obtained.

Finally, voltage vector v is converted to a
force vector f via the transformation

10 f = cv,

where the first three elements of f are the measured
values of the three orthogonal components of the
applied force and the last three elements are the
values of the components of the applied torque , and
15 c is a 6X8 matrix whose elements were obtained

through calibration using applied forces and torques
of known magnitude.

VI. Limb Coupling Cuff

A limb coupling cuff, labelled 376 in Figure 3,

20 acts as the physical interface between the human
limb (in the present application, the arm) and the
manipulator, and has the function of transferring
loads from the manipulator to the limb. Preferably,
cuff 376 is made of plastic or plaster or styrofoam

25 and molded to the shape of the limb. The goal of
the cuff is to provide the stiff est, most solid
connection between the manipulator and the limb, so

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that manipulator control over the limb is maximized,
without substantially sacrificing user comfort. A
handle which is gripped by the user can be used in
place of the limb coupling cuff.

5 VI I . Count erba lances

The load of the linkage structure described in
Section I with the equipment of Sections II — VI , is
unbalanced about the rotational axes of several
joints. For example, in Figure 3, the moment

10 produced by the portion of the linkage (as equipped
with particle brakes, reducers, position sensors,
and the force-torque sensor) to the right of joint
314 exceeds the moment produced by the portion to
the left, giving the manipulator arm the tendency to

15 tilt downward on the right side. This effect causes
the human subject to feel a weight load at the
manipulator endpoint. At joint 308, a similar
imbalance exists. Finally, the two upper
parallelograms of the upper linkage do not balance

20 the lower parallelogram about joint 304.

To balance the load about each of these
rotational axes, counterbalance weights are placed
at appropriate locations in the manipulator
structure. First, certain particle brakes

25 themselves act as counterbalances. Particle brakes
B2 and B3 act as counterbalances for the rotational
axis of joint 308, brakes B4 and B5 act as
counterbalances for the rotational axis of joint
314, and brake B5 acts as a counterbalance for the

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rotational axis of joint 304. In addition, lead
weights used solely for the purpose of
counterbalancing supplement the particle brakes.
Lead weights 378 and 380 attached to links 340 and
5 364 act to counterbalance loads about the rotational
axes of joints 308 and joints 314 and 304,
respectively.

Applications

In a general sense, the manipulator of the

10 invention is a system for controllably resisting the
movement of a limb. Accordingly, the manipulator
can be used in a number of different applications.

One such application is that in which the
manipulator is used as an exercise machine. The

15 microcomputer 104 of Figure 1 is programmed to

display a moving target 13 00 on the display monitor
108, as shown in Figure 9. Simultaneously, the
subject 102 attempts to pursue the target 1300 by
moving his/her arm, as indicated by a crosshair 13 02

20 displayed on the monitor 108. The motion of the
target can be programmed to correspond to certain
arm movements, so that certain muscles can be
exercised. Moreover, the amount of resisting force
can be controlled by varying coil currents in the

25 particle brakes so as to vary resistance levels in
the exercise machine.

Another application of the manipulator is in
physical therapy. Here, the manipulator would be
used in conjunction with a microcomputer and display

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monitor as above , with the goal being the
rehabilitation of certain muscles. Of course, in
each of these applications, the use of the display
monitor for pursuit tracking tasks is not necessary.
5 The manipulator could be used in the manner that
conventional weight-training and exercise machines
are used.

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CLAIMS

1. A system for resisting limb movement
comprising:

a) a plurality of links joined by joints to
5 form a linkage system between a fixed

point in space and a movable end point of
said linkage system;

b) a limb coupler for coupling a limb to said
end point; and

10 c) a plurality of brakes for resisting

trans lational link movement in at least
three mutually orthogonal directions and
for resisting rotational link movement
about at least three mutually orthogonal

2. The system of Claim 1 wherein the linkage
system moves in the direction of a force
applied to said end point,

3. The system of Claim 1 including a plurality of
20 position sensors for sensing the degree of

translational and rotational movement of said
links about said joints in the three directions
and three axis.

4. The system of Claim 3 including a plurality of
25 velocity sensors for sensing the rate of said

translational and rotational movement.

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5. The system of Claim 4 including a computer

wherein the sensed positions and rates generate
signals which are coupled to at least one brake
to vary the amount of resistance generated by

6. A system of Claim 1 wherein the brake effects <
resistance in a direction opposite to the
endpoint velocity direction.

7. A system of Claim 1 wherein the linkage system

of links and joints.

8. A system of Claim 1 wherein the brake further
comprises a first cylinder with a first
diameter coupled to the brake , a second

15 cylinder with a second diameter which is wider

than said first diameter coupled to a rotating
joint of the linkage system and a cable with
one end connected to the second cylinder, said
cable is wrapped around the first cylinder to

20 amplify the brake torque.

9. A system of claim 8 wherein the brake further
includes a position sensor, said sensor is
connected to the end of the cable opposite to
the end connected to the second cylinder.

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10. A system of Claim 9 wherein at least one brake
is positioned on a linkage as a counterbalance
weight.

11. A system for resisting limb movement
5 comprising:

a) a plurality of links joined by joints to
form a linkage system including at least
three parallelograms of links and joints
between a fixed point in space and a

10 movable end point of said linkage system;

b) a limb coupler for coupling a limb to said
end point;

c) a plurality of brakes for resisting
translational link movement in at least

15 three mutually orthogonal directions and

for resisting rotational link movement
about at least three mutually orthogonal

d) a plurality of position sensors for
20 sensing the degree of translational and

rotational movement of said links about
said joints in the three directions and

e) a plurality of velocity sensors for

25 sensing the rate of said translational and

rotational movement;

f ) a first cylinder with a first diameter
coupled to the brake;

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12.

g) a second cylinder with a second diameter
which is wider than said first diameter
coupled to a rotating joint of the linkage
system;

h) a cable with one end connected to the
second cylinder, said cable is wrapped
around the first cylinder to amplify the
brake torque; and

i) a computer wherein the sensed positions
and rates generate signals which are
coupled to at least one brake to vary the
amount of resistance generated by the
brake .

A method for resisting limb movement comprising
the steps of:

a) coupling a limb to a movable end point of
a linkage system, said linkage system
including a plurality of links joined by
joints to form a linkage system between a
fixed point in space and said movable end
point of said linkage system;

b) sensing the degree of translation and
rotation of said links;

c) sensing the rate of translation and
rotation of said links;

d) resisting translational link movements in
at least three mutually orthogonal
directions ;

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e) resisting rotational link movements about
at least three mutually orthogonal axes;
and

f ) varying the translational resistances and
5 the rotational resistances in accordance

with the sensed positions and rates of
movement of the links.

13, A method as recited in Claim 12 wherein the
resistance is effected in a direction opposite

10 to the end point velocity direction.

14. A method as recited in Claim 12 wherein the
linkage system further comprises at least three
parallelograms of links and joints.

15. A method as recited in Claim 12 wherein the
15 brake further comprises a first cylinder with a

first diameter coupled to the brake, a second
cylinder with a second diameter which is wider
than said first diameter coupled to a rotating
joint of the linkage system and a cable with
20 one end connected to the second cylinder, said

cable is wrapped around the first cylinder to
amplify the brake torque.

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102

100

106

104

MANIPULATOR

I t

PREPROCESSING
ELECTRONICS

1 t

MICROCOMPUTER

MONITOR
I

r-108

I02a

100

206

POSITIONAL
VELOCITY

SENSORS

FORCE

TORQUE

SENSOR

208

PROCESSOR

106

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3/6

202

506

500
504

502

508

JL.

204

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344

714

710

716

-/_TO LINE
342 FIG.3

712

336

600

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o

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INTERNATIONAL SEARCH REPORT

International Application No
I. CLASSIFICATION OF SUBJECT MATTER (i f several classification symbols apply, indicate ail) 6
According to International Patent Classification (IPC) or to both National Classification and IPC

Int. CI. 5 A61F5/01; B25J13/08;

G05B13/00

PCT/US 92/00369

n. FIELDS SEARCHED

Classification System

Int. CI. 5

Minimum Documentation Searched 7

Classification Symbols

A61F

Documentation Searched other than Minimum Documentation
to the Extent that such Documents are Included in the Fields Searched*

HI. DOCUMENTS CONSIDERED TO BE RELEVANT 9

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Full text of "USPTO Patents Application 10597633"

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